1. Field of the Invention
The invention relates to a technique of providing new and useful impact tool.
2. Description of the Related Art
An impact tool is provided with an angular positioning device which positions a hammer bit in its circumferential direction with respect to a tool body during hammering operation. For example, Japanese non-examined laid-open Patent publication No. 11-104974 discloses an impact tool having such an angular positioning device. The angular positioning device in the above publication is disposed in a tip end region of a barrel which forms a tool body. In the angular positioning device, a locking member is disposed between a barrel and a tool holder for holding the hammer bit. The locking member is normally connected via a spline fit with respect to the tool holder and can be connected to or disconnected from the barrel via engagement of projections and recesses. The position of the tool bit is adjusted by appropriately rotating the tool bit together with the tool holder in a state in which the locking member is disconnected from the barrel. Thereafter, the tool bit is fixedly positioned in the adjusted position by connecting the locking member to the barrel again.
In a construction in which the angular positioning device is disposed in the tip end region of the barrel, the angular positioning device is located close to the tool bit to be positioned. Therefore, the operability of the angular positioning device can be advantageously enhanced, but on the other hand, the angular positioning device is affected by dust of a workpiece (concrete) which is generated during hammering operation. Specifically, a connection between the locking member and the tool holder and a connection between the locking member and the barrel are caused to be susceptible to wear by entry of dust. Therefore, each of members of the angular positioning device including the barrel is formed from wear-resistant materials such as ferrous materials in order to enhance durability. Further, the impact tool which is held by the user's hand in hammering operation is desired to be as light as possible, and particularly as for the barrel having a relatively large volume, such is highly desired. However, if the barrel is formed from lighter materials than ferrous materials, such as nonferrous metals and synthetic resins, the required wear resistance cannot be ensured. In this point, further improvement is required.
On the other hand, Japanese non-examined laid-open Patent Publication No. 2000-127066 discloses an impact tool having an impact absorption mechanism for absorbing an impact during an idle driving movement. The known impact absorption mechanism is designed such that, when a tool bit is held away from a workpiece and a striker performs a striking movement, an elastic element is subjected to a load of an intermediate element which moves forward together with the striker, and thereby absorbs an impact caused by the striking movement of the striker. In other words, the impact absorption mechanism in the known impact tool is designed such that mainly one elastic element is subjected to an impact caused by the striker during idle driving. Therefore, the elastic element is subjected to a heavy load, so that further improvement is required in durability.